The orthogonal frequency division multiplexing (OFDM) scheme is a well-known, high-speed data transmission scheme for next-generation communication technologies. In a conventional OFDM receiver, after a received signal is demodulated to baseband and converted to the digital domain by analog-to-digital converters, its in-phase and quadrature signals are fed to a Fast Fourier Transform (FFT) engine, which computes the in-phase and quadrature Fourier coefficients for further signal processing. The FFT algorithm is well known to minimize the computational resources in generating the Fourier coefficients from a Discrete Fourier Transform (DFT), and many efficient FFT algorithms are widely used in OFDM receivers.
However, multipliers are required in FFT algorithms and their number grows according to N log N, where N denotes the number of input sample points or output Fourier coefficients. As demand for higher data rates and bandwidths in mobile communications has grows, complexity of the FFT processor must also increase to cope with a larger number of OFDM channels.
In light of the short comings in the FFT algorithm processing complexity, a novel OFDM-based receiver, which requires no multiplication when computing the Fourier coefficients, is described herein. This receiver is based on the bandpass sampling technique combined with delta-sigma modulation to demodulate and digitize an RF signal to baseband in a form of high-sampling rate bit streams. The down-converted in-phase and quadrature output signals are clocked at a high sampling rate, comparable to the carrier frequency that modulates the RF signal, and the in-phase and quadrature outputs are bi-level digital signals, having values of 1 or −1. The bi-level digital signals can be fed to the DFT processor, in which the complex exponents, commonly referred to as ‘the twiddle factors’ can be either added to or subtracted from an accumulator depending on the instantaneous value of the input digital signals, 1 or −1, respectively. As a result, no multiplication is required in this OFDM receiver, thereby improving the DFT resource complexity and processing latency as addition and subtraction are processed faster than multiplication.